Yes, 彩虹勇者獎勵計劃 is completely free and it doesn't have any in-app purchases or subscriptions.
Not enough reviews to make a reliable assessment. The app needs more user feedback.
彩虹勇者獎勵計劃 is free.
To get estimated revenue of 彩虹勇者獎勵計劃 app and other AppStore insights you can sign up to AppTail Mobile Analytics Platform.